Data from: Asymmetric energetic costs in reciprocal-cross hybrids between carnivorous mice (Onychomys)

Aerobic respiration is a fundamental physiological trait dependent on coordinated interactions between gene products of the mitochondrial and nuclear genomes. Mitonuclear mismatch in interspecific hybrids may contribute to reproductive isolation by inducing reduced viability (or even complete inviability) due to increased metabolic costs. However, few studies have tested for effects of mitonuclear mismatch on respiration at the whole organism level. We explored how hybridization affects metabolic rates in closely related species of grasshopper mice (genus Onychomys) to better understand the role of metabolic costs in reproductive isolation. We measured metabolic rate across a range of temperatures to calculate basal metabolic rates (BMR) and cold-induced metabolic rates (MRc) in O. leucogaster, O. torridus, and O. arenicola, and in reciprocal F1 hybrids between the latter two species. Within the genus, we found a negative correlation between mass-specific BMR and body mass. Although O. arenicola was smaller than O. torridus, hybrids from both directions of the cross resembled O. arenicola in body mass. In contrast, hybrid BMR was strongly influenced by the direction of the cross: reciprocal F1 hybrids were different from each other but indistinguishable from the maternal species. In addition, MRc was not significantly different between hybrids and either parental species. These patterns indicate that metabolic costs are not increased in Onychomys F1 hybrids and, while exposure of incompatibilities in F2 hybrids cannot be ruled out, suggests that mitonuclear mismatch does not act as a primary barrier to gene flow. Maternal matching of BMR is suggestive of a strong effect of mitochondrial genotype on metabolism in hybrids. Together, our findings provide insight into the metabolic consequences of hybridization, a topic that is understudied in mammals.

有氧呼吸（Aerobic respiration）是一项依赖于线粒体基因组（mitochondrial genomes）与核基因组（nuclear genomes）的基因产物协同互作的基础生理特征。种间杂种（interspecific hybrids）中的核质不匹配（mitonuclear mismatch）可能通过提升代谢成本，引发生存力降低（甚至完全致死），进而促成生殖隔离（reproductive isolation）。然而，目前鲜有研究在整体生物水平上检验核质不匹配对呼吸作用的影响。本研究以亲缘关系较近的爪鼠属（Onychomys）蝗虫小鼠为研究对象，探究杂交事件如何影响其代谢率，以期更深入地理解代谢成本在生殖隔离中发挥的作用。

我们在一系列温度梯度下测定代谢率，以计算白斑爪鼠（O. leucogaster）、托氏爪鼠（O. torridus）、沙生爪鼠（O. arenicola），以及后两者之间的互交F1杂种（reciprocal F1 hybrids）的基础代谢率（BMR）与冷诱导代谢率（MRc）。

在该属内，我们发现体质量特异性基础代谢率与体质量呈负相关关系。尽管沙生爪鼠的体型小于托氏爪鼠，但两个杂交方向的杂种体质量均与沙生爪鼠相近。与之形成对比的是，杂种的基础代谢率则强烈受杂交方向的影响：互交F1杂种彼此间存在显著差异，但均与其母本物种无明显区别。此外，杂种与任一亲本物种的冷诱导代谢率均无显著统计学差异。

上述结果表明，爪鼠属的F1杂种并未出现代谢成本升高的情况；尽管无法排除F2杂种中出现遗传不相容性的可能，但该结果提示核质不匹配并未作为基因流（gene flow）的主要障碍。基础代谢率的母本匹配效应暗示，线粒体基因型（mitochondrial genotype）对杂种的代谢过程具有显著影响。综上，本研究结果为杂交的代谢后果提供了重要见解，而这一研究主题在哺乳动物类群中仍有待进一步探索。